Cadmium standard cell



Dec. 17, 1957 G. D. VINCENT CADMIUM STANDARD CELL Filed July 20, 1956 INVENTOR. GEORGE D VINCENT ATTONE Y United CADMIUM STANDARD CELL George D. Vincent, Newport, R. 1., assiguor to The Eppley Laboratory, Inc., Newport, R. L, a corporation of Rhode Island Application July 20, 1956, Serial No. 599,044

7 Claims. (Cl. 136-88) My present invention relates to standard cells and more particularly to a cadmium standard cell of the portable, unsaturated type.

The principal object of the present invention is to provide a cell construction which will greatly reduce the variations in E. M. F. due to the leakage of mercury past the retaining plug.

Another object of the present invention is to provide a cell construction in which the positive leg is provided with a double plug septum for retaining the mercury in place.

With the above and other objects and advantageous features in view, my invention consists of a novel arrangement of parts more fully disclosed in the detailed description following in conjunction with the accompanying drawings and more particularly defined in the appended claims.

In the drawings:

Fig. 1 is an enlarged vertical section of a standard cell embodying my invention.

In practice, the volt is established by a cell or battery. This usually comprises a glass vessel in the form of an H in which the constitutents of the cell are contained. The

materials in a cadmium standard cell of the portable, unsaturated type are held in place by various means such as the plug or septum shown in Eppley Patent No. 2,613,234, issued October 7, 1952. These plugs or septa have been made of various materials such as porcelain or cork. The Eppley patent shows a septum made of nonporous plastic material in the form of a split ring and covered at the sides and bottom by a double layer of linen. The purpose of these plugs is to prevent the cadmium hearing liquid of the amalgam from getting over to the mercury-mercurous sulfate electrode, to prevent the murcury and mercurous sulfate from mixing, and to keep the electrode material in both legs of the H in place and in contact with their respective platinum wire electrode.

Since the mercury of the positive electode is a mobile liquid, some pressure is necessary on the plug securing that system. Shocks, jars, and increased pressure due to temperature rises causes the mercury to leak past the plug barrier. Such mercury, forced past the plug, does not return to place even after a restoration of the original temperature. This loose mercury in the electrolyte portion'of the cell has not been regarded as a source of serious inaccuracy. However, I have found that when the quantity of mercury is sufficient to nearly completely fill the plug, it does cause variations in E. M. F. which range from .001% to .02%. The effect is usually such as to reduce the total E. M. F. of the cell and is more marked when the mercury is on the positive side.

Tests using high speed of response devices, such as a cathode ray oscilloscope, have disclosed that there is an oscillatory disturbance of the E. M. F. of a standard cell having such loose mercury when it is mechanically jarred. Such disturbances resemble damped oscillations on the screen of the oscilloscope. In the worst cases, with a considerable amount of loose mercury in the cell,

' the formation of drops or pools.

the first swing, which is the largest, amounts to about .05 volt. The period of oscillation is about .01 second and the disturbance dies out in less than .2 second, .1 second being average. 7

When the standard cell is used with a direct current galvanometer of comparatively long periods (1 second or more), such oscillatory disturbances are without effect. However, several modern applications use standard cells in electronic and other circuits of higher speeds. These are affected by such disturbances. In these devices the standard cell contributes microphonic noises to the circuit and makes it unstable.

The present invention therefore comprises an improved standard cell designed to eliminate these disturbances by retaining the loose mercury in a form which will prevent Referring to the drawing illustrating my invention, the standard cadmium cell illustrated therein comprises a container 10 made of glass or other suitable material. It comprises two vertical links 11 and 12 connected by an integral cross tube 13. The

main body of the cell may be filled with the solution of cadmium sulfate 14. In the form shown, the lower portion of the left hand limb 11 acts as the positive electrode and the lower portion of the right hand limb 12 acts as a negative electrode.

At the bottom of the limb 12, forming the negative electrode, is a layer of cadmium amalgam in which the platinum connecting wire 16 is embedded. Above the amalgam 15 is a layer of cadmium sulfate solution 17 surmounted by the plug 18. The positive electrode, at the bottom of the limb 11, comprises a layer of mercury 19 in which the connecting wire 20 is mounted. Above the mercury 19 is a layer of mercurous sulfate 21 surmounted by the plug 22. s

The above is the conventional construction of a cadmium standard cell. The plugs 18 and 22 are preferably of the type shown in Patent No. 2,613,234 hereinabove referred to. These comprise rings of non-porous synthetic plastic material covered with two thicknesses of porous material 'such as linen to provide a porous diaphragm held in place by the ring. The improvement of the present invention consists of the additional structure in the positive limb 11 positioned above the plug 22. This comprises a second plug or septum 23 at a distance of .5 to 2 cm., depending on the type of cell, above the normal plug 22. The space between is approximately half filled with uncompressed gray mercurous sulfate 24, containing free mercury but no free globules of mercury, and the other half is filled with a filler such as long fibred cotton 25. This second plug 23 is pushed down far enough to prevent the materials between it and the lower plug 22 from mixing when the cell is inverted or shanken, but not enough to compress the mercurous sulfate.

Tests show that the disturbing electromotive forces are generated when the globules of loose mercury are broken up or run together, or when mechanical motions cause changes in the contour of the surface of the mercury drops or pools. In the construction of the present invention, the additional mercurous sulfate above the plug 22, which is in a paste form, serves as a depolarizer on the surface of any mercury that has leaked past the plug 22. The mercury is also physically confined to some extent so as to prevent the free flow from droplets to globules. This serves to stabilize the voltage and prevents mechanical disturbances from producing waves or distortions of the mercury surface.

The construction shown is easy to install in any standard cell. Tests show that the micriphonic noise from free mercury is reduced by a factor of about 100. Also variations in the E. M. F. due to the loose mercury, observable by conventional means such as relatively long period direct current galvanometers, are substantially eliminatsdq Patented Dec. 17, 1957' a 3 While [have described a cadmium standard cell with a pantioularrt-ype of plug; it isobvious that the invention. can be readily applied to any other standard cell using any type of plug or septum. Other advantages of the present invention will he-readily apparent to a person skilledjirr-thear-t: I a

1. In a standard cell consisting of an H-shapedtubedm whiclr thepositiveelectrode comprises a'layerofi mercury and'ta'l'ayer of mercuroussulfate above said merouryandt, aplug between said merourous sultate'and the electrolyte iii tlie-cell a second plugmounted in thecell above-saidt firstplug and? in spaced relationthereto; and) a' .depolauicing agent and a fibrous fill'er disposed within: said: space between said plugs.

2. In a standard cell consisting ofzana l-tlsshaped-z tube. inwhich: thepositive electrode comprises: a; layer; of rnereury' and a; layer of mercurous: sulfate.= above; mercury and a-plug between.saidzmercurousisulfatmandi the electrolyte; in. thezcell, a, second plug :mountedz imthe: cell above saidl first? plug andl in: spaced: relation. thereto; and a depolarizing agent; and a fibrous. filler disposed; within said: space. between. said plugs,. said; depolarizin agent comprising mercurousrsulfate.

31 Inca standard cell. consisting ofzan H-shaped tube in, which thepositive. electrode. comprises. a; layer; of; mercury and a. layer of mercurous sulfate. above said: mercury and a plug between said mercurous; sulfate; and the electrolyte in the cell, a second plugmounted'inathe cell above said. first plug and; in: spaced: relation; thereto, and afibrous filler. disposed; within said! space. between said plugs; said: filler. comprising longi fihredz cotton.

4. In at standard cell consisting of an hl-sliaped' tube int which the positive".v electrode comprises: a: layer of mercury: and a. layer of mercurous sulfater. above said mercury and-a: plug between saidsmercurouszsulfatc and the-electrolyte-im the cell; a second plug-mounted in the cell above said first plug and in spaced relation thereto, andl a depolarizing agent and a fibrous filler. disposed withimsaid' space between! said plugs, said. filler comprising long fibred cotton.

51 In a standard cell'consisting of arr H-shaped tube in. which the positive electrode comprises a layer of mercury and a' layer of mercurous sulfate" above said 4 mercury and a plug between said mercurous sulfate and theelectrolyteinthe cell,.a.seco.nd plug mountedinlhta. cell above said first plug and in spaced relation thereto, and a depolarizing agent and a fibrous filler disposed within said space between said plugs, said depolarizing agent comprising mercurous sulfate and said fibrous filler comprising long fibred cotton.

6. A means for reducing variations in E. M. F. due to mercury leakage-ina. cadmium standard'cellof the portable unsaturated type, said.means comprising astandard cellhaving an Hashaped' tubeiifn which the positiveelectrode comprises a layer of mercury and a layerof mercurous sulfate above said mercury and a plug between said mercurous sulfate and the'electrolytein thecell, a

second plug mounted in said. cell above said first plug and in spaced relation thereto, and a depolarizing agent and a fibrous filler disposed within said space between said plugs, whereby loose mercury that has passed through said first: plug willbe substantially: confined toand. depolarized within said space.

7. A means for reducing variations in E, M. F. due to mercury leakage in a cadmiumstandard: cell of the portablemnsaturated type,.said.means.comprising a stanchard: cell. havingv an. Hrshapedtubeini which the positive electrode comprises a layer of mercury, and: a layen of mercurous: sulfate. above said: mercury and a. plug between; said; mercurous: sulfate and they electrolyte in: the. celLa second plug mountedrin said' cell above said first: plugand; inspacedzrelationthereto, and: a depolarizing gent; and a fibrous filler'disposed withinsaidispace be tween said; plugs, said. depolarizing agent comprising mercurous. sulfate; and] said fibrousfiller comprising long fibred; cotton; whereby loose. mercury that has passed; through said first plug will be substantially confined to, and depolarized within said space.

References Cited in the file of: this patent.

UNITED STATES PATENTS 1,760,178: Seitz. May 27, 1,9302

2,613,234 Eppley Oct. 7, 1952.

FOREIGN PATENTS 628,372 Great Britain Aug. 26, 1949 

1. IN A STANDARD CELL CONSISTING OF AN H-SHAPED TUBE IN WHICH THE POSITIVE ELECTRODE COMPRISES A LAYER OF MERCURY AND A LAYER OF MERCUROUS SULFATE ABOVE SAID MERCURY AND A PLUG BETWEEN SAID MERCUROUS SULFATE AND THE ELECTROLYTE IN THE CELL, A SECOND PLUG MOUNTED IN THE CELL ABOVE SAID FIRST PLUG AND IN SPACED RELATION THERETO, AND A DEPOLARIZING AGENT AND A FIBROUS FILLER DISPOSED WITHIN SAID SPACE BETWEEN SAID PLUGS. 